Mulitple USRP Stream Confusion

GNU Radio
1

Hello!

I am having trouble trying to create a continuous stream of complex
shorts from multiple (2) X310 USRPs (each running 2 channels) over a
single 1gigE switch (at a very low sampling rate); currently it appears
as though I can only stream from one USRP at a time and I can’t seem to
figure out why. I should note I don’t have this problem running each
USRP on its own dedicated network (but unfortunately that won’t be
possible moving forward).

To date, I have been using the rx_multi_samples example provided with
UHD (source 003.007.002). I dont seem to have any issue connecting to
both USRPs and setting the parameters via the args=addr0=192.168.10.2,
addr1=192.168.10.3 command. It is just that when I call rx_stream->recv
only the lights on the USRP which was listed first in args turn on. The
subdev spec and channel selection for each USRP is set to “A:A B:A” and
“0,1” and the incoming data from rx_stream is two channels of complex
shorts (not 4 like I would expect from 2 USRPs).

Do I have to initiate the streams differently or am I missing something?

Thanks!

-Andrew

2

Hey Andrew,

First, that subdev seems off – I’d assume it’s something like “A:0
B:0”? Next, I’m not even sure what you mean you set the channels to
“0,1” on both devices. You should have 1 streamer, with a channel
setting of “0,1,2,3”. The ‘args’ string seems correct.

Does this help?

M

3

Hello Martin,

Thanks for the response.

I should have mentioned that the subdev spec was set to A:A B:A because
I am using the basic RX boards. Trying “0:A 0:B” instead gives the
following error: “0:A is not a valid rx subdevice specification on
mboard 0. possible values are: [A:AB, A:BA, A:A, A:B, B:AB, B:BA, B:A,
B:B].”

Your suggestion to set the channel as 0,1,2,3 seemed to work perfectly
(not sure how I missed that) as now I am getting four complex shorts out
of my setup (an example of what is now in the buffer is shown below):

(-3,-2)(3,0)(-1,0)(1,0)
(2,-1)(0,0)(-3,0)(-2,0)
(3,5)(1,0)(-1,0)(-1,0)
(4,-2)(-4,0)(-1,0)(2,0)

In getting the channels to stream however, I ran across another strange
occurrence. After looking at the FFT data it appears as though the
following commands only set the frequency of the first channel:

uhd::tune_request_t tune_request(freq);
usrp->set_rx_freq(tune_request);

Channels 1,2, and 3 all show single peaks centered at 0 Hz in the FFT
window. I was able to correct this by directly setting the frequency of
each channel independently (as shown below) , but I was under the
impression that when you create the usrp devices to begin with it should
apply commands across all channels?

uhd::tune_request_t tune_request(freq);
usrp->set_rx_freq(tune_request, 0);
usrp->set_rx_freq(tune_request, 1);
usrp->set_rx_freq(tune_request, 2);
usrp->set_rx_freq(tune_request, 3);

Thanks again! This is really a great product and I look forward to
getting more acquainted with what it can do.

-Andrew

From: discuss-gnuradio-bounces+andrew.daigle=removed_email_address@domain.invalid
[discuss-gnuradio-bounces+andrew.daigle=removed_email_address@domain.invalid] on behalf of
Martin B. [[email protected]]
Sent: Tuesday, September 30, 2014 5:04 PM
To: [email protected]
Subject: Re: [Discuss-gnuradio] Mulitple USRP Stream Confusion

Hey Andrew,

First, that subdev seems off – I’d assume it’s something like “A:0
B:0”? Next, I’m not even sure what you mean you set the channels to
“0,1” on both devices. You should have 1 streamer, with a channel
setting of “0,1,2,3”. The ‘args’ string seems correct.

Does this help?

M

On 30.09.2014 13:01, Daigle, Andrew - 1008 - MITLL wrote:

To date, I have been using the rx_multi_samples example provided with
Thanks!

-Andrew

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4

No, since you can easily have independent channels inside a multi-usrp
block, gain and frequency parameters need to be set for each

channel. You can see how this works when you do the same thing from
within GRC, and look at the generated code.

On 2014-10-01 08:54, Daigle, Andrew - 1008 - MITLL wrote:

(3,5)(1,0)(-1,0)(-1,0)
usrp->set_rx_freq(tune_request, 0);
To: [email protected]

M

On 30.09.2014 13:01, Daigle, Andrew - 1008 - MITLL wrote:

Hello! I am having trouble trying to create a continuous stream of complex
shorts from multiple (2) X310 USRPs (each running 2 channels) over a single 1gigE
switch (at a very low sampling rate); currently it appears as though I can only
stream from one USRP at a time and I can’t seem to figure out why. I should note I
don’t have this problem running each USRP on its own dedicated network (but
unfortunately that won’t be possible moving forward). To date, I have been using
the rx_multi_samples example provided with UHD (source 003.007.002). I don’t seem
to have any issue connecting to both USRPs and setting the parameters via the
args=“addr0=192.168.10.2, addr1=192.168.10.3” command. It is just that when I call
rx_stream->recv only the lights on the USRP which was listed first in args turn
on. The subdev spec and channel selection for each USRP is set to “A:A B:A” and
“0,1” and the incoming data from rx_stream is two channels of complex shorts (not
4 like I would expect from 2
USRPs). Do I have to initiate the streams differently or am I missing
something? Thanks! -Andrew
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